1. Field of the Invention
The present invention relates to a combustor that supports an operation with a hydrogen-containing gas, and a method for operating the combustor while suppressing NOx emission.
2. Description of the Related Art
Fuel rich-lean combustion based on a diffusive combustion system is one of methods for suppressing NOx emission while ensuring reliability of a burner. The fuel rich-lean combustion is performed in such a manner that fuel is supplied through a single system. In operation, the fuel is supplied to a primary combustion zone provided at a head portion of the combustor and is then burned (fuel rich combustion) under a fuel rich condition so that an increase in the flame temperature is suppressed, thereby suppressing generation of NOx. Next, unburned fuel from the primary combustion zone flows down into a secondary combustion zone provided downstream of the combustor. Then, the unburned fuel is supplied with air in the secondary combustion zone, where the unburned fuel and the air are rapidly burned (fuel lean combustion) under a fuel lean condition.
However, since a flame is formed long in the primary combustion zone, it is necessary to cool the liner wall surface of a combustion chamber. Although air can be used to cool the liner wall surface of the combustion chamber, such an air supply will lead to an increase in the concentration of oxygen. With an increase in the concentration of oxygen, the flame temperature becomes high. Thus, NOx emission may be increased.
To avoid this, a technique for supplying fuel through two fuel systems has been disclosed in JP-8-210641-A. In this publication, fuel is supplied in the direction of the axis of the combustion chamber so that the flame length in the primary combustion zone is appropriately controlled.